在监测项目上，我需要计算来自脉冲计的脉冲。我已经找到了一些解决方案，我一直在努力适应我的需求。
这是在Raspberry Pi上运行的python脚本：
#!/usr/bin/env python
import RPi.GPIO as GPIO
import datetime
import sys
import signal
from subprocess import check_output
#verbose = True # global variable
############################################################################################################
############################################################################################################
def printusage(progname):
print progname + ' <gpio-pin-number> <filename> [debug]'
print 'Example usage: '
print progname + ' 23 /path/to/mylogfile'
print progname + ' 23 /path/to/mylogfile debug'
sys.exit(-1)
def signal_handler(signal, frame):
if verbose:
print('You pressed Ctrl+C, so exiting')
GPIO.cleanup()
sys.exit(0)
def readvalue(myworkfile):
try:
f = open(myworkfile, 'ab+') # open for reading. If it does not exist, create it
line=subprocess.check_output(['tail','-f','-1',f])
elmts=line.split(" ")
value = int(elmts[2])
except:
value = 0 # if something went wrong, reset to 0
#print "old value is", value
f.close() # close for reading
return value
def writevalue(myworkfile,value):
f = open(myworkfile, 'a')
f.write((str(datetime.datetime.now())+' '+str(value)+'\r\n')) # timestamp
f.close()
############################################################################################################
############################################################################################################
######### Initialization
#### get input parameters:
try:
mygpiopin = int(sys.argv[1])
logfile = sys.argv[2]
except:
printusage(sys.argv[0])
verbose = False
try:
if sys.argv[3] == 'debug':
verbose = True
print "Verbose is On"
else:
printusage(sys.argv[0])
except:
pass
#### if verbose, print some info to stdout
if verbose:
print "GPIO is " + str(mygpiopin)
print "Logfile is " + logfile
print "Current value is " + str(readvalue(logfile))
#### setup
GPIO.setmode(GPIO.BCM)
GPIO.setup(mygpiopin, GPIO.IN, pull_up_down = GPIO.PUD_DOWN)
signal.signal(signal.SIGINT, signal_handler) # SIGINT = interrupt by CTRL-C
########## Main Loop
while True:
# wait for pin going up
GPIO.wait_for_edge(mygpiopin, GPIO.RISING)
# read value from file
counter=readvalue(logfile) + 1
if verbose:
print "New value is", counter
# write value to file
writevalue(logfile,counter)
# and wait for pin going down
GPIO.wait_for_edge(mygpiopin, GPIO.FALLING)
############################################################################################################
############################################################################################################
我想要注册最后一个索引，然后递增它，但到目前为止我测试的所有内容都将循环停留在索引1上。
我无法使用“更重”的方法来查找最后一行，例如浏览整个文件，因为随着时间的推移，它只会变得越来越重，我不能错过一个脉冲。
我对编程很陌生，所以感谢你的帮助！
编辑：结果文件如下所示：
2016-10-08 16:54:23.072469 1
2016-10-08 16:54:23.462465 1
2016-10-08 16:54:23.777977 1
2016-10-08 16:54:24.010045 1
2016-10-08 16:54:24.194032 1
2016-10-08 16:54:24.388120 1
2016-10-08 16:54:24.549389 1
2016-10-08 16:54:24.737994 1
2016-10-08 16:54:24.959462 1
2016-10-08 16:54:25.164638 1
2016-10-08 16:54:25.351850 1
2016-10-08 16:54:25.536655 1
2016-10-08 16:54:25.716214 1
2016-10-08 16:54:25.794152 1
2016-10-08 17:06:13.506531 1
2016-10-08 17:06:14.097642 1
2016-10-08 17:06:14.211579 1
2016-10-08 17:06:15.237852 1
2016-10-08 17:06:15.752239 1
2016-10-08 17:06:16.320419 1
2016-10-08 17:06:16.842906 1
2016-10-08 17:06:17.391121 1
2016-10-08 17:06:17.851521 1
2016-10-08 17:06:18.444486 1
2016-10-08 17:06:18.858358 1
答案 0 :(得分：0)
要读取大文件的最后一行，请选择文件末尾附近的位置并阅读。如果那里没有换行符，请稍微再看一遍。
然后找到最后一个换行符，剩下的就是你的最后一行。
EXPECTED_MAX_LINE_SIZE = 500 # this should be both small enough and big enough
def get_last_line(f):
end = f.seek(0, os.SEEK_END) # detect file size
pos = end-EXPECTED_MAX_LINE_SIZE
if pos < 0: pos = 0
f.seek(pos, os.SEEK_SET)
end_of_file = f.read(EXPECTED_MAX_LINE_SIZE)
# TODO: check if '\n' is not there and read some more
return end_of_file.splitlines()[-1]
答案 1 :(得分：0)
你的逻辑过于复杂，如果你将不同时间运行脚本，只需将最后一个索引存储在一个单独的文件中不断覆盖：
def next_index(index):
with open(index, 'a+') as f: # open for reading. If it does not exist, create it
val = int(next(f, -1)) + 1 # first run value will be 0
open(index,"w").write(str(val)) # overwrite
return val
如果在其他地方创建了值，那么只需在那里写，只需确保用w覆盖之前的值。
答案 2 :(得分：0)
我不认为这就是Padraic Cunningham的意思，但我设法通过使用两个文件来解决我的问题，一个用于记录更新的索引值，另一个用于存储值：
#!/usr/bin/env python
import RPi.GPIO as GPIO
import datetime
import sys
import signal
#verbose = True # global debug variable
############################################################################################################
def printusage(progname): #show how to use the script
print progname + ' <gpio-pin-number> <index file> <store file> [debug]'
print 'Example usage: '
print progname + ' 23 /path/to/mylogfile /path/to/storefile'
print progname + ' 23 /path/to/mylogfile /path/to/storefile debug'
sys.exit(-1)
def signal_handler(signal, frame): #exiting the script
if verbose:
print('You pressed Ctrl+C, so exiting')
GPIO.cleanup()
sys.exit(0)
def readvalue(myworkfile):
try:
f = open(myworkfile, 'ab+') # open for reading. If it does not exist, create it
line=f.readline() #read the first and only line of the file
elmts=line.split(" ") # the format is <yyyy-mm-dd hh:mm:ss.ssssss indexvalue>
value = int(elmts[2]) #get the index value
except:
value = 0 # if something went wrong, reset to 0
#print "old value is", value
f.close() # close for reading
return value
def writevalue(myworkfile,value):
f = open(myworkfile, 'w') #overwrite the value
f.write((str(datetime.datetime.now())+' '+str(value))) # timestamp + data
f.close()
def store_value(index_file,index_value):
f=open(index_file, 'a+')
f.write(str(datetime.datetime.now())+' '+str(index_value)+'\r\n') #store timestamp + data
f.close()
############################################################################################################
######### Initialization
#### get input parameters
try:
mygpiopin = int(sys.argv[1])
logfile = sys.argv[2]
storefile=sys.argv[3]
except:
printusage(sys.argv[0])
verbose = False
try:
if sys.argv[4] == 'debug':
verbose = True
print "Verbose is On"
else:
printusage(sys.argv[0])
except:
pass
if verbose: #### if verbose, print some info to stdout
print "GPIO is " + str(mygpiopin)
print "Logfile is " + logfile
print "Storefile is " + storefile
print "Current value is " + str(readvalue(logfile))
#### SETUP
GPIO.setmode(GPIO.BCM)
GPIO.setup(mygpiopin, GPIO.IN, pull_up_down = GPIO.PUD_DOWN)
signal.signal(signal.SIGINT, signal_handler) # SIGINT = interrupt by CTRL-C
########## Main Loop #####
while True:
GPIO.wait_for_edge(mygpiopin, GPIO.RISING) # wait for pin going up
counter=readvalue(logfile) + 1 # read value from file and increment index
if verbose:
print "New value is", counter
writevalue(logfile,counter) # write value to logfile
store_value(storefile,counter) # store value in storefile
GPIO.wait_for_edge(mygpiopin, GPIO.FALLING) # and wait for pin going down
############################################################################################################
感谢您的帮助！